The development of new, cost-competitive processes that utilize renewable resources as feedstocks is vital for a sustainable economy. These processes also represent important milestones toward the goal of reducing the United States' dependence on foreign oil. Introduction of such processes not only avoids the use of more petroleum, but also has the potential to provide substantial energy savings, and reduce greenhouse gas emissions. Although biobased syntheses of certain commercially significant compounds such as 1,3-propanediol have been reported, there are comparatively few reported approaches to compounds related to terephthalic acid. See, e.g., G. A. Kraus, Clean—Soil, Air, Water, 36, 648 (2008); W. H. Gong (BP Corporation N. A., Inc.), PCT WO 09/064,515; WO 08/63703; U.S. Ser. No. 07/940,097).
Terephthacidic acid, or 1,4-biscarboxybenzene is a precursor for the widely used polyester PET, used to make clothing and plastic bottles. Terephthalic acid is currently produced by the oxidation of para-xylene in air using cobalt and manganese salts to catalyze the reaction.
The Diels-Alder reaction of pyrones such as coumalic esters with activated alkynes has been described. See, e.g, K. Afarinka et al., Tetrahedron, 48, 9111 (1992) and T. A. Bryson et al., J. Org. Chem., 42, 2930 (1977). As shown in Scheme 1, wherein A is an activating group, the reaction of alkynes with methyl coumalate (1) involves a cycloaddition to produce bicyclo[2.2.2]octadiene intermediate 2 that loses carbon dioxide to directly form the substituted benzene. Delaney et al., have utilized this reaction to produce phenols. P. M. Delaney et al., Tetrahedron, 64, 866 (2007).
The reaction of activated alkenes, such as acrylates or acrylonitrile, with methyl coumalate produces bicyclic lactone 3, wherein A is an alkoxycarbonyl or CN, that cannot go directly to an aromatic ring by loss of carbon dioxide. One way to construct aromatic rings via this intermediate is to catalytically dehydrogenate adduct 3 under conditions that lead to loss of carbon dioxide. Y. Matsushita et al., Synth. Commun., 24, 3307 (1994).